Chuanjiang Qin

Retarding the crystallization of PbI2 for highly reproducible planar-structured perovskite solar cells via sequential deposition

On a planar substrate the sequential deposition of CH3NH3PbI3 perovskite is optimized by retarding the crystallization of PbI2. This strategy overcomes the problem of incomplete conversion and uncontrolled particle sizes of perovskite in the absence of mesoporous scaffolds, greatly increasing the film reproducibility. Highly efficient and reproducible planar-structured perovskite solar cells were obtained with the best efficiency of 13.5%, average efficiency of 12.5% and a small standard deviation of 0.57 from a total of 120 cells.

A dopant-free hole-transporting material for efficient and stable perovskite solar cells

An efficient pristine hole-transporting material (HTM), tetrathiafulvalene derivative (TTF-1), was introduced into perovskite solar cells, without the use of p-type dopants. As compared to cells based on well-known p-type doping with spiro-OMeTAD, perovskite solar cells based on dopant-free TTF-1 performed with a comparable efficiency of 11.03%; moreover, the stability of the dopant-free TTF-1 based cell was greatly improved two fold in air at a relative humidity of ∼40%. To the best of our knowledge, this is the first case of perovskite solar cells employing a dopant-free HTM based on a tetrathiafulvalene derivative yielding an efficiency over 11%. The present finding paves the way for the development of efficient dopant-free HTMs for perovskite solar cells, which promotes the advancement of cost-effective and practical perovskite solar cells.

Hybrid interfacial layer leads to solid performance improvement of inverted perovskite solar cells

Despite the sky-rocketing efficiencies being reported for perovskite solar cells (PSSCs) with several different configurations recently, it is as yet unclear which configuration will prove beneficial over others. In this work, we report a novel, inverted PSSC with the configuration of FTO/NiO/meso-Al2O3/CH3NH3PbI3/PCBM/BCP/Ag. The first implementation of the hybrid interfacial layer of an ultrathin NiO compact layer (10–20 nm) plus an inert mesoporous Al2O3 (meso-Al2O3) scaffold, featuring high optical transparency and specific dual blocking effect, leads to minimal light absorption loss and interfacial recombination loss. The device performance has been significantly improved with respect to the control PSSCs without the meso-Al2O3 layer. Synchronized improvements in photovoltage, photocurrent and fill factor lead to a high efficiency of >13%, which is the highest reported so far for NiO based PSSCs. Small hysteresis and stable power output under working conditions have been demonstrated for this type of solar cells. The results also highlight the general and critical importance of interfacial control in PSSCs, and their effects on device performance.

Highly compact TiO2 layer for efficient hole-blocking in perovskite solar cells

A uniform and pinhole-free hole-blocking layer is necessary for high-performance perovskite-based thin-film solar cells. In this study, we investigated the effect of nanoscale pinholes in compact TiO2 layers on the device performance. Surface morphology and film resistance studies show that TiO2 compact layers fabricated using atomic layer deposition (ALD) contain a much lower density of nanoscale pinholes than layers obtained by spin coating and spray pyrolysis methods. The ALD-based TiO2 layer acts as an efficient hole-blocking layer in perovskite solar cells; it offers a large shunt resistance and enables a high power conversion efficiency of 12.56%.

Squaraine Dyes for Dye‐Sensitized Solar Cells: Recent Advances and Future Challenges

In the past few years, squaraine dyes have received increasing attention as a sensitizer for application in dye-sensitized solar cells. This class of dyes not only leaves open a good opportunity to afford conventional high performance dyes but also holds great promise for applications in transparent solar cells due to its low absorption intensity in the eye-sensitive region. This review provides a summary of the developments on squaraine dyes in the field of dye-sensitized solar cells and the opportunities used to improve their overall energy conversion efficiency. In particular, the main factors responsible for the low values of open-circuit voltage, short-circuit photocurrent and fill factor are discussed in detail. Future directions in research and development of near-infrared (NIR) organic materials and their applications are proposed from a personal perspective.

Improvement of spectral response by co-sensitizers for high efficiency dye-sensitized solar cells

Simple donor–π–acceptor organic dyes, denoted as HC3, HC4, and HC5, were synthesized as co-sensitizers for black dye based dye-sensitized solar cells. By tuning the electron-donating moieties and side alkyl chain lengths of the co-sensitizers, the spectral photoresponse was greatly enhanced from the UV to the entire visible region. The short circuit current density was significantly improved by 8.5% in the BD + HC5 cell with respect to the cell with BD only, and consequently a high efficiency of 11.6% was achieved.

Tuning the Electrical and Optical Properties of Diketopyrrolopyrrole Complexes for Panchromatic Dye-Sensitized Solar Cells

A series of metal-free organic dyes that were bridged by a diketopyrrolopyrrole moiety and were composed of indoline and triphenylamine as donor groups and furan and benzene as conjugated spacer groups were designed and synthesized for use in dye-sensitized solar cells (DSCs). The photophysical properties, electrochemical properties, and performance of the DSCs were related to the structure of their corresponding dyes. Their absorption spectra broadened upon the introduction of the indoline and heterocyclic furan moieties through fine-tuning of their molecular configuration. The overall conversion efficiencies of DSCs that were based on these dyes ranged from 5.14-6.53%. Among the four dyes that were tested, indoline-based ID01 and ID02 showed higher efficiencies (6.35% and 6.53%) as a result of their improved light-harvesting efficiency and larger electron driving force. The ID01 dye, which contained an indoline moiety as an electron donor and a furan group as a π-conjugated linker, showed an excellent monochromatic incident-photon-to-current-conversion efficiency (IPCE) spectrum (350-650 nm) with a maximum value of 78% in the high plateau region and an onset value close to 800 nm. Intensity-modulated photovoltage spectroscopy (IMVS) and impedance spectroscopy (IS) revealed that dyes that contained benzene conjugation spacers suppressed the charge-recombination rate more efficiently than dyes that contained furan spacers, thereby resulting in improved photovoltage.

A Novel Organic Sensitizer Combined with a Cobalt Complex Redox Shuttle for Dye-Sensitized Solar Cells

A novel donor-π-acceptor organic dye (HIQ7) was used in dye-sensitized solar cells with a cobalt redox shuttle. The cells showed broad incident monochromatic photon-to-current conversion efficiency spectra covering the entire visible range and extending into the near-infrared region.

Coordinated shifts of interfacial energy levels: insight into electron injection in highly efficient dye-sensitized solar cells

Coordinated shifts on the order of ∼100 meV were found in the interfacial energy levels of ruthenium dye molecules and the conduction band of nano-crystalline TiO2. The shifts were induced by potential-determining additives used in highly efficient dye-sensitized solar cells. The observation of comparable shifts of interfacial energy levels in dye/TiO2 films is beyond the conventional understanding of the varied quantum efficiency of interfacial electron injection, which had been derived under the assumption of the band shift only in TiO2. Based on general physical concepts, we advanced the understanding of the electron injection mechanism and attributed the variable electron injection efficiency to the influence of potential-determining additives on the interfacial electronic structures of both the dyes and TiO2. Our results revealed that the interfacial dipole layer affected the electronic coupling between the donor states in photo-excited dyes and the acceptor states in TiO2, which led to changes in electron injection. The present model also explains the correlation between the radiative recombination, an important loss mechanism in solar cells, of photo-excited states of the anchored dye/TiO2 in operational cells and that of free dye molecules in solution. We also found the amount of coordinated shifts to be most likely related to the number of COOX groups in ruthenium dyes and metal-free organic dyes. This relationship implies that the effect of coordinated shifts in ruthenium dyes/TiO2 is one of the most probable reasons why these dyes enable higher performance than do metal-free organic dyes, in which the latter only have relatively small coordinated shifts. This discovery provides deeper insight into the interfacial electron injection mechanism and points out the importance of the realignment effect on interfacial energy levels in highly efficient dye-sensitized solar cells.

Enhanced Photovoltaic Performances of Dye-Sensitized Solar Cells by Co-Sensitization of Benzothiadiazole and Squaraine-Based Dyes

Dye-sensitized solar cells (DSSCs) based on a donor-acceptor-donor oligothienylene dye containing benzothiadiazole (T4BTD-A) were cosensitized with dyes containing cis-configured squaraine rings (HSQ3 and HSQ4). The cosensitized dyes showed incident monochromatic photon-to-current conversion efficiency (IPCE) greater than 70% in the 300-850 nm wavelength region. The individual overall conversion efficiencies of the sensitizers T4BTD-A, HSQ3, and HSQ4 were 6.4%, 4.8%, and 5.8%, respectively. Improved power conversion efficiencies of 7.0% and 7.7% were observed when T4BTD-A was cosensitized with HSQ3 and HSQ4, respectively, thanks to a significant increase in current density (JSC) for the cosensitized DSSCs. Intensity-modulated photovoltage spectroscopy results showed a longer lifetime for cosensitized T4BTD-A+HSQ3 and T4BTD-A+HSQ4 compared to that of HSQ3 and HSQ4, respectively.